1. Technical Field of the Invention
The present invention relates to a liquid detecting method and liquid detecting system for detecting a liquid in a liquid container used on a liquid ejector.
2. Description of the Related Art
The conventional liquid ejectors include, as representative examples, an inkjet recorder having a inkjet recording head for image recording. As other liquid ejectors, there are an apparatus having a color-material ejection head for use in the manufacture of a color filter such as of a liquid display, an apparatus having an electrode-material (conductor paste) ejection head for use in forming an electrode for an organic EL display, a surface-emission display (FED) or the like, an apparatus having an bio-organic ejection head for use in the manufacture of a bio-chip and an apparatus having a sample-ejection head as a precision pipette, for example.
The inkjet recorder as a representative example of the liquid ejector is mounted, on a carriage, with an inkjet recording head having pressure generating means for pressurizing a pressure generating chamber and a nozzle opening for ejecting pressurized ink in the form of an ink droplet.
The inkjet recorder is structured to continue printing by continuously supplying the ink in an ink container to the recording head through a flow path. The ink container is structured as a removal cartridge which the user is allowed to exchange when the ink is consumed up, for example.
Conventionally, the cartridge ink consumption managing methods includes a method of managing ink consumption by a calculation of totalizing, on software, the number of ejections at the recording head or the amount of ink sucked in maintenance, a method of managing a time the ink is actually consumed a predetermined quantity by attaching a liquid-level-detection electrode to the ink cartridge, and so on.
However, in the method of managing the ink consumption by a calculation of totalizing, on software, the number of ejections of ink droplets or the amount of ink, there is the following problem. Of heads, there are those having weight variations between ink droplets ejected. The weight variations between ink droplets do not have an effect upon image quality. However, the ink cartridge is charged with ink in an amount with a margin, taking into consideration of cumulative ink consumption errors due to the variations. Accordingly, there arises a problem that the amount of ink corresponding to the margin is left in a certain individual.
Meanwhile, the method of managing with electrodes the time the ink is consumed up is to detect the actual amount of ink, allowing for managing the ink remaining quantity with reliability. However, this relies upon the electric conductivity of ink in detecting an ink level, thus having a defect that detectable ink is limited in kind or electrode seal structure is complicated. Meanwhile, the electrode uses usually a material of precious metal well in electric conductivity and high in corrosion resistance, mounting up the manufacture cost of the ink cartridge. Furthermore, the need of attaching two electrodes increases the manufacturing process with a result of increased manufacture cost.
There is an apparatus developed to solve such a problem, disclosed as a piezoelectric device in JP-A-2001-146024. This piezoelectric device is to detect a liquid remaining quantity correctly but eliminated the necessity of a complicated seal structure so that it can be attached and used on a liquid container.
Namely, according to the piezoelectric device described in JP-A-2001-146024, the ink remaining quantity in the ink cartridge can be monitored by utilization of the nature that there is a change in the resonant frequency to the residual vibration signal occurring due to the residual vibration (free vibration) on a piezoelectric-device vibration portion after forcibly vibrated on a drive pulse, between the cases of a presence of ink in a space opposed to the piezoelectric-device vibration portion and of an absence of ink therein.
FIG. 16 shows an actuator structuring a conventional piezoelectric device. This actuator 106 has a substrate 178 having a circular opening 161 nearly in the center, a vibration plate 176 arranged on one surface (hereinafter, referred to as a “surface”) of the substrate 178 in a manner covering the opening 161, a piezoelectric layer 160 arranged on a side close to the surface of the vibration plate 176, an upper electrode 164 and a lower electrode 166 that sandwich the piezoelectric layer 160 at respective sides, an upper electrode terminal 168 electrically coupled to the upper electrode 164, a lower electrode terminal 170 electrically coupled to the lower electrode 166, and an auxiliary electrode 172 arranged between the upper electrode 164 and the upper electrode terminal 168 and electrically coupling the both together.
The piezoelectric layer 160, the upper electrode 164 and the lower electrode 166 have respective circular portions as their main portions. The circular portions of the piezoelectric layer 160, upper electrode 164 and lower electrode 166 form a piezoelectric device.
The vibration plate 176 is formed on the surface of the substrate 178 in a manner covering the opening 161. A vibration region for actual vibration of the vibration plate 176 is determined by the opening 161. A cavity 162 is formed by an area of vibration plate facing the opening 161 and the opening 161 in the substrate (cavity forming member) 178. The opposite surface of substrate 178 to the piezoelectric device (hereinafter, referred to as a “back surface”) faces the inward of the ink container. Due to this, the cavity 162 is structured in contact with the liquid (ink). Incidentally, the vibration plate 176 is attached for liquid-seal on the substrate 178 in order not to leak liquid to the surface of the substrate 178 even if liquid intrudes in the cavity 162.
In the actuator 106 of the prior art, the residual vibration (free vibration) at the vibration portion, caused after forcibly vibrating the vibration portion through the application of a drive pulses to the piezoelectric device, is to be detected as an inverse electromotive force by means of the same piezoelectric device. Thus, the ink remaining quantity in the ink container can be detected by utilization of a change in the residual vibration state of the vibration portion before and after a passage of the liquid level in the ink container beyond the arrangement position of the actuator (exactly, cavity 162 position).
Meanwhile, in FIGS. 6 to 8 in JP-A-2001-146024, there is shown a structure that the cavity has a length in a direction of extracting the upper and lower electrode made longer than its length in a direction orthogonal thereto.
The conventional actuator (piezoelectric device) 106 mentioned above is structured to expose the cavity 162, attached in the container wall of the container body 181 of the ink cartridge 180 as shown in FIG. 17 and for receiving the ink as a subject-of-detecting, to an ink reservoir space in the interior of the ink container 180.
However, in the conventional actuator (piezoelectric device) 106, because of a structure to expose the cavity 162 to the ink reservoir space in the ink container 180, if an air bubble occurs in the ink of the ink cartridge 180 due to vibration or so, the air bubble easily intrudes into the cavity 162 of the actuator 106. In case the air bubble intrudes into the cavity 162 and stays there, the resonant frequency to residual vibration to be detected by the actuator 106 advances in time regardless of a sufficient amount of remaining ink in the ink cartridge 180. Thus, there is a problem of an erroneous detection of a reduced ink remaining quantity because the liquid level passed the position of actuator 106.
Meanwhile, in case the cavity 162 of actuator 106 is reduced in size in order to detect the liquid-level passage timing with accuracy, ink meniscus is readily formed in the cavity 162. Consequently, there is a problem that the ink is to remain in the cavity 162 despite the liquid level passed the position of cavity 162 as the ink is consumed, resulting in an erroneous decision of not yet passed the liquid level beyond the position of actuator 106 and there is a sufficient amount of remaining ink.
In order to solve the above problem, it can be considered to provide a liquid sensor with an ink supply path for supplying ink to the cavity and an ink discharge path for discharging ink from the cavity, as proposed in Japanese Patent Application No. 2004-122763 filed by the present applicant.
However, in the liquid sensor having the ink supply path and ink discharge path, there is a problem as in the following.
Namely, in the state the in cartridge ink is continuously consumed during head cleaning or print operation, fluid flow (ink and/or air) takes place in the cavity of the liquid sensor.
There is a phenomenon that the ink put on the cavity wall surface is not easily discharged even when the remaining ink decreases into a state that air is to pass the interior of the cavity.
In case to detect a presence/absence of ink in the state ink is put on the cavity wall surface in this manner, there is a possibility of a decision of a presence of ink despite it is in a state normally to be decided as an absence of ink.